The invention disclosed herein pertains generally to a constant pressure air storage installation for a gas turbine power station, and more particularly to an apparatus for preventing blowouts of the constant pressure air storage installation.
Constant pressure air storage installations for gas turbine power stations usually include relatively large subterranean cavities beneath the power stations, which cavities are used to store compressed air. The volumes of the air cavities used in constant pressure air storage installations are usually only about one-third the volumes of the cavities used in variable air pressure storage instalations, in which variable air pressure storage installations the pressure is allowed to vary within certain limits. Consequently, the cost of providing a cavity for a constant pressure air storage installation is much lower than the cost of providing a cavity for a variable air pressure storage installation.
To maintain constant air pressure in the air storage cavity of a constant pressure air storage installation, the air storage cavity usually includes a water inlet in fluid communication with a column of water contained within a standpipe. The water which enters the cavity through the water inlet compensates for the volume of air discharged from the cavity during a discharging operation. The height of the water column, which water column is usually in fluid communication with a water basin located at the surface of the ground, corresponds to the static pressure to be maintained in the cavity. In present day installations the air cavity is typically located at a depth of 600-800 m below the ground, which implies that the static pressure at the base of the column of water in the standpipe is in the range 60-80 bar. During the air changing of the cavity, the water in the cavity and in the standpipe is forced upwards under pressure into the basin, while upon discharging air from the cavity water runs from the basin into the cavity to re-establish the required static pressure.
It has been found in the operation of gas turbine air storage installations that during the charging of the cavity the water forced out of the cavity into the standpipe releases dissolved air, thus creating air bubbles whose volumes rapidly increase during their upward ascent within the standpipe. The existence of the air bubbles reduces the density of the column of water in the standpipe, causing a drop in the static pressure at the base of the water column and of the water in the cavity. In an extreme case, the column of water may be blown out of the standpipe by the greater pressure of the charging air in the cavity and the cavity completely emptied of water.
In comparison with the normal rate at which air dissolves in still water, full air saturation of the water in the cavity takes place more rapidly due to the high degree of turbulence produced in the water during the charging and discharging operations, which turbulence enables nearly all of the particles of the water in the cavity to come into contact with the air in the cavity. The amount by weight of air absorbed by the water is proportional to the static pressure which, as noted above, is between 60 and 80 bar. The following examples serve to illustrate the amounts of air dissolved in water at atmospheric pressure and in an air storage cavity at 60 bar pressure:
(1) at an air pressure of 1 bar and a temperature of 10.degree. C., 1 m.sup.3 water (=1000 kg) contains 29.2 g air; and
(2) at a pressure of 60 bar and a temperature of 10.degree. C., 1 m.sup.3 water contains 1.7 kg air, i.e., approximately 58 times the amount by weight of air dissolved in water at 1 bar pressure. At atmospheric pressure, the 1.7 kg of air has a volume of approximately 1.32 m.sup.3. A mixture of water and air depressurized from a pressure of 60 bar to atmospheric pressure thus contains more air than water.
When water saturated with air rises upwardly from the air cavity through the water column, the water from the air cavity releases dissolved air, that is, the air comes out of solution and forms bubbles of gradually increasing size because of the decreasing hydrostatic pressure. The average density of the water column therefore becomes constantly smaller and the static pressure of the water at the base of the water column and in the cavity decreases correspondingly. This may lead, if suitable measures are not taken, to a blow-out of the cavity and of the water column.
A known method for preventing blow-outs is to extend the standpipe containing the water column in a U-shaped arc beneath the bottom of the cavity. The deepest penetration of the standpipe into the ground must be at least 0.15 h beneath the prevailing water level in the cavity, where h is the effective pressure height, i.e., the difference between the geodetic height of the upper water level in the water basin and the water level in the cavity. If h=600 m, then this means that the standpipe, which is already 600 m long, will have to be extended downwardly in a U-shaped arc by another 90 m, which represents an unacceptable additional construction cost.
Accordingly, a primary object of the present invention is to provide a relatively simple and inexpensive apparatus for preventing blow-outs in the compressed air storage installations of gas turbine power stations.
Apparatus for preventing a blow-out of a constant pressure air storage installation of a gas turbine power station, according to the present invention, includes a subterranean air storage cavity, a water basin which is substantially at ground level, and a standpipe connecting the water basin to the subterranean cavity. At least an upper portion of the standpipe is arranged obliquely with respect to the horizontal. The present invention also includes at least one ventilation pipe which is connected to, and in fluid communication with, the upper portion of the standpipe. An upper end of the at least one ventilation pipe is arranged above the water level of the water basin.